Radiation is a very important tool for the modification of polymer materials through degradation, grafting, and cross-linking. Radiation's effects on carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, and pectin were investigated to enhance their use for recycling these bioresources and thereby reducing environmental pollution. These carbohydrates were degraded by irradiation, and biological activities such as antimicrobial activity, promotion of plant growth, suppression of heavy metal stress, and phytoalexins induction were induced. The induction of phytoalexins by using radiation-degraded carbohydrates was studied. The pectic fragments obtained by irradiation with 1000 kGy (10 kGy/h) from 60Co were most effective for induction of glyceollins (a phytoalexin in soybeans) and induced almost the same amount of glyceollins as pectin-PGase. The degraded alginate was effectively used either in solution (4%) or powder for growth promotion of rice field. Similar behavior for growth promotion of plants was reported for chitosan, carrageenan, and lignocellulose extracts. © 2010 Elsevier Inc. All rights reserved.